[redland-dev] Redland for Revolution & questions

[rodney tamblyn]

Hi everyone,

Together with a fellow student (Noel Garside) here I've been working on 
porting Redland to a set of DLLs so they can be called from Runtime 
Revolution (Rev) programming environment (http://www.runrev.com).  The 
DLLs include Rev glue and wrapper code allowing callbacks, exchange of 
variables, and exposing of the Redland API within the Rev scripting 
environment.   Things have been going pretty well, we've got Redland 
compiling fine under Windows, including the extra header files and glue 
files to expose wrapped Redland functions within Revolution.  Once 
everythings going fine on Windows we'll take a look at doing same on 
OSX.

I'm going to use Redland as part of research project I'm working on to 
create a collaborative image annotation application for use in medical 
teaching settings.

So far we've been able to create a world, storage object (memory) and 
model, parse in a URI, add statements, and print out a model (using 
librdf_model_print).

At the moment I have a problem which I'm hoping list members may be 
able to help with.  If I create a memory storage I'm able to complete 
the example above successfully.  However if change the storage params 
to create a hashes database, and repeat, the persistent database is 
created successfully on disk, but Rev crashes when calling 
librdf_model_print.  I've also tried creating a serializer and calling 
serializer_print_model_to_file with same results.  Executing the same 
code directly from C as a compiled application (eg example1.exe) runs 
fine.

If I create an example which just reads a model from a hashes database 
on disk, and feed it the database created by Rev, it prints the model 
out fine.  This shows that there's nothing wrong with the model, or 
storage, but there's something going on in the serializer when called 
from Rev.  I think what may be happening is that the serializer is 
raising an error, but I have not implemented an error callback message 
(world_set_error).  Perhaps this is then returning control from the 
external to Rev in such a way as to cause an memory exception error.

I'm pretty new to C programming (although very experienced in scripting 
environments) so I'm hoping someone kind could provide some C examples 
showing:

- an example "hello world" redland error handling function - this could 
for example just print the error to stderr
- code to setup this function (i.e appropriate syntax to configure this 
via world_set_error)
- ideally, and example which will cause an error (so that I can test 
this is working correctly).

I can then modify the example to send callback messages to Revolution 
when errors are raised. Once I've got error reporting working for the 
above, I'll implement functions for serializer_set_error and 
serializer_set_warning as this is where I think my problem is.

A couple more questions:
1) - if an error occurs and world_set_error has not been set, what 
happens?

2) - are warnings and logger actually utilized in the library?  I 
notice quite a lot of messages being written to stdout and stderr, and 
just wondered if these shouldn't more appropriately be sent to the 
logger?

Thanks for help and suggestions in advance.

~ Rodney
--
Rodney Tamblyn
44 Melville Street
Dunedin
New Zealand
+64 3 4778606
http://rodney.buzzword.com/
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